Question

1. for the human body to function normally, blood ph must be maintained between 7.35 and 7.45. when carbon dioxide levels in the blood rise, the ph of the blood decreases. the body then reacts to restore normal blood ph. which of the following best explains why this process is referred to as a negative feedback loop?

a. carbon dioxide is removed from the body.
b. it is harmful to have a decrease in blood ph.
c. while a person is running, the brain sends signals to muscles.
d. as carbon dioxide in the blood decreases, blood ph returns to normal.
clear selection

Explanation:

Step1: Understand negative feedback loop

A negative feedback loop is a mechanism that reverses a deviation from the set point. In this case, when carbon dioxide levels rise (decreasing blood pH as \(CO_2 + H_2O
ightleftharpoons H_2CO_3
ightleftharpoons H^+ + HCO_3^-\), more \(H^+\) means lower pH), and then when \(CO_2\) decreases (as in option D), the body acts to restore the normal blood pH.

Step2: Analyze each option

• Option A: Just stating \(CO_2\) is removed is a general biological process (cellular respiration and exhalation), not specifically a negative - feedback - loop description.
• Option B: A decrease in blood pH is harmful, but this option does not describe the loop that restores the balance.
• Option C: Signals from the brain to muscles during running is a motor control process (related to movement), not a pH - regulation negative - feedback loop.
• Option D: When \(CO_2\) (which affects pH) decreases, blood pH returns to normal. This shows the loop: deviation (change in \(CO_2\) and pH) → response (pH return) that counteracts the initial change (negative feedback).

Answer:

D. As carbon dioxide in the blood decreases, blood pH returns to normal.